The present invention relates generally to the art of respiratory gas analysis, and particularly to a gas sampling system for conducting respiratory gases from a patient to a respiratory gas monitoring device.
Respiratory gas monitoring is used extensively in medical and clinical settings. Gas monitors are an invaluable tool in providing care providers with information relating to a patient""s metabolism. Medical personnel are often interested in the relative and absolute amounts of oxygen and carbon dioxide in the respired gases to determine a patient""s respiratory function and oxygen metabolization. Respiratory gas monitoring is also important during surgery. Anesthesia must be carefully administered. An overdose of anesthesia, or a lack of oxygen, could lead to brain damage or death. On the other hand, if the anesthesiologist does not administer enough anesthesia the patient may become aware during the surgical procedure and experience severe pain and discomfort.
Respiratory gasses are delivered from a patient to the gas monitor by way of a gas sampling system. A patient""s respiratory gasses are directed into the gas sampling system by a respiratory output device such as an oral/nasal cannula, a nasal cannula, an endotracheal tube, a tracheostomy tube, or a mask. The gases are conducted from the respiratory output device to the monitor by a connecting gas sampling tube. Gas monitors often display the inhaled and exhaled concentrations of oxygen (O2), carbon dioxide (CO2), nitrous oxide (N2O), and/or anesthetic agents. Alarms are typically sounded when a gas concentration falls outside a predetermined range of values.
A common problem with the aforementioned gas sampling system relates to the CO2 detector in the monitor. In addition to conducting respired gasses to the monitor, gas sampling tubes may also direct damaging moisture into the CO2 detector. In one approach that has been considered, gas sampling systems were equipped with water trap and gas flow shut-off mechanisms. Typically, the valve mechanism is disposed in the connector coupling the gas sampling tube to the gas monitor. While the valve mechanism prevents water from damaging the CO2 detector, it is also adapted to substantially restrict the flow of respiratory gasses if the valve is exposed to too much moisture. When this occurs, the gas sampling system must be replaced. In another approach that has been considered, the moisture problem has been addressed by placing a dryer mechanism in the connector adjacent to, or proximate to, the respiratory output device (e.g., the mask, cannula, or etc.). Unfortunately, this approach also has several drawbacks.
In one scenario, the patient is disposed in an incubator or in an oxygen tent, while the gas monitor is disposed downstream in a room-temperature environment. Of course, the environment in the oxygen tent or incubator is typically warmer and more humid than the room temperature environment. As the respired gasses propagate from the warmer environment to the room-temperature environment, condensate forms in the section of the gas sampling tube located in the room-temperature environment. Thus, the dryer mechanism disposed proximate the patient is ineffective, and the water trap shut-off valve located adjacent the gas monitor is quickly closed.
In another scenario, the patient is wearing a nasal cannula and is disposed in a cooler environment. When the patient exhales, the respired gas is at body temperature and saturated with water. Condensate typically forms in the cannula. The dyer mechanism disposed in the gas sampling tube adjacent to the cannula will remove some of the moisture. However, as the respiratory gasses propagate from the patient to the gas monitor, additional condensate will form in the gas sampling tube. Obviously, the dryer mechanism disposed near the patient cannot remove the additional condensate. Again, the water trap shut-off valve located adjacent the gas monitor will close in a relatively short period of time.
What is needed is a gas sampling system that is equipped to successfully remove condensate that forms along the entire length of the gas sampling tube. What is also desirable is a gas sampling system that substantially removes water before it is directed into the valve mechanism.
The gas sampling system of the present invention addresses the aforementioned problems. The gas sampling system of the present invention is equipped to remove condensate that forms along the entire length of the gas sampling tube. The present invention is configured to remove water in the respired gasses before the water is directed into the valve mechanism. In so doing, the gas sampling system of the present invention has an effective operational life-span that is far superior to the related systems described above.
One aspect of the present invention is a gas sampling system for conducting respiratory gases from a patient respiratory gas output mechanism to a respiratory gas monitoring device. The respiratory gas monitoring device is equipped with a monitor input connector. The gas sampling system includes an input connector configured to couple the gas sampling system to the patient respiratory gas output mechanism. A gas sampling tube is coupled to the input connector. The gas sampling tube is configured to conduct the respiratory gases from the patient to the gas monitoring device. An output connector couples the gas sampling tube to the monitor input connector. An output dryer tube is coupled between the gas sampling tube and the output connector. The output dryer tube is characterized by a tube length and a relative moisture removal efficiency. The relative moisture removal efficiency is dependent on the tube length. The tube length is selected to limit the moisture content of the respiratory gasses being directed into the respiratory gas monitor.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.